Radio repeater trunking (time sharing of a single repeater communications channel among many users) is well-known. Early trunking systems used analog control signals while some more recent systems have utilized digital control signals. Control signals have been utilized on a dedicated control channel and/or on different ones of the working channels for various different reasons and effects. A non-exhaustive but somewhat representative sampling of publications and patents describing typical prior art trunked radio repeater systems is identified below:
U.S. Pat. No. 3,898,390, Wells et al (1975) PA0 U.S. Pat. No. 4,392,242, Kai (1983) PA0 U.S. Pat. No. 4,534,061, Ulug (1985) PA0 U.S. Pat. No. 4,649,567, Childress (1987) PA0 U.S. Pat. No. 4,658,435, Childress et al (1987) PA0 U.S. Pat. No. 4,716,407, Borras et al (1987) PA0 JAPAN 61-102836 (A) Ishikawa (May 1986) PA0 U.S. Pat. No. 3,292,178, Magnuski (1966) PA0 U.S. Pat. No. 3,458,664, Adlhoch et al (1969) PA0 U.S. Pat. No. 3,571,519, Tsimbidis (1971) PA0 U.S. Pat. No. 3,696,210, Peterson et al (1972) PA0 U.S. Pat. No. 3,906,166, Cooper et al (1975) PA0 U.S. Pat. No. 3,936,616, DiGianfilippo (1976) PA0 U.S. Pat. No. 3,970,801, Ross et al (1976) PA0 U.S. Pat. No. 4,001,693, Stackhouse et al (1977) PA0 U.S. Pat. No. 4,010,327, Kobrinetz et al (1977) PA0 U.S. Pat. No. 4,012,597, Lynk, Jr. et al (1977) PA0 U.S. Pat. No. 4,022,973, Stackhouse et al (1977) PA0 U.S. Pat. No. 4,027,243, Stackhouse et al (1977) PA0 U.S. Pat. No. 4,029,901, Campbell (1977) PA0 U.S. Pat. No. 4,128,740, Graziano (1978) PA0 U.S. Pat. No. 4,131,849, Freeburg et al (1978) PA0 U.S. Pat. No. 4,184,118, Cannalte et al (1980) PA0 U.S. Pat. No. 4,231,114, Dolikian (1980) PA0 U.S. Pat. No. 4,309,772, Kloker et al (1982) PA0 U.S. Pat. No. 4,312,070, Coombes et al (1982) PA0 U.S. Pat. No. 4,312,074, Pautler et al (1982) PA0 U.S. Pat. No. 4,326,264, Cohen et al (1982) PA0 U.S. Pat. No. 4,339,823, Predina et al (1982) PA0 U.S. Pat. No. 4,347,625, Williams (1982) PA0 U S. Pat. No. 4,360,927, Bowen et al (1982) PA0 U.S. Pat. No. 4,400,585, Kamen et al (1982) PA0 U.S. Pat. No. 4,409,687, Berti et al (1983) PA0 U.S. Pat. No. 4,430,742, Milleker et al (1984) PA0 U.S. Pat. No. 4,430,755, Nadir et al (1984) PA0 U.S. Pat. No. 4,433,256, Dolikian (1984) PA0 U.S. Pat. No. 4,450,573, Noble (1984) PA0 U.S. Pat. No. 4,485,486, Webb et al (1984) PA0 U.S. Pat. No. 4,578,815, Persinotti (1985) PA0 U.S. Pat. No. 4,594,591 to Burke PA0 U.S. Pat. No. 4,517,561 to Burke et al PA0 U.S. Pat. No. 4,152,647 to Gladden et al PA0 U.S. Pat. No. 4,612,415 to Zdunek et al PA0 U.S. Pat. No. 4,427,980 to Fennel et al PA0 U.S. Pat. No. 4,553,262 to Coe PA0 Unlimited prestored plans PA0 Unlimited source and destination groups per plan PA0 Regrouping at the plan or destination group level PA0 Advanced user interface PA0 Automatic support of multiple sites PA0 Fast regrouping PA0 Fast activation/deactivation PA0 Up to 8 regroups per radio
There are many actual and potential applications for trunked radio repeater systems. However, one of the more important applications is for public service trunked (PST) systems. For example, one metropolitan area may advantageously use a single system of trunked radio repeaters to provide efficient radio communications between individual radio units within many different agencies. As is well-known to those familiar with trunking theory, a relatively small number of radio repeaters can efficiently service all of the needs of a public service organization within a given geographic area if they are trunked (i.e., shared on an "as-needed" basis between all potential units).
Before modern trunked radio repeater systems were developed, mobile radio transceivers were provided with crystal controlled frequency synthesizers providing a limited number of fixed transmit/receive channels -- and the various channels were assigned for use by different "groups" of radio transceivers. Referring to FIG. 1, for example, fixed channels might be assigned as follows:
channel A to police squad A, PA1 channel B to police squad B, PA1 channel C to rescue squad/paramedics, PA1 channel D to snow removal equipment, PA1 channel E to municipal vehicles, PA1 channel F to fire squad A, and PA1 channel G to fire squad B.
Every mobile transceiver in a group was typically capable of communicating with other members of its group and with a central dispatcher) over its assigned communications channel. In addition, several additional channels were typically provided for "cross-group" communications. For example, an additional channel H might be used to permit members of police squad A and police squad B to communicate with one another -- while still permitting squad A to use its privately and exclusively assigned channel A to communicate with other members of squad A without disturbing members of squad B. Similarly, an additional channel I might be provided for communications between fire squads A and B and the rescue squad; and a further channel J might be provided for communications between members of police squad A and/or B, the rescue squad, and members of one or both fire squads.
This type of arrangement, although certainly providing private and reliable communications, had some severe disadvantages. One disadvantage was that the "cross-group" channels were usually under-utilized (since most routine communications take place within a group), but often became extremely congested during disasters or emergencies requiring coordination between members of different groups. Moreover, "cross-group" communications typically required some degree of advanced cooperation on the part of each and every member involved (e.g., each user had to properly switch his transceiver to the "cross-group" channel or be sure his "scanning" type transceiver was enabled to monitor that "cross-group" channel). Suppose, for example, that a police officer in police squad A wished to communicate with a rescue vehicle in the rescue squad. The police officer could switch his transceiver to communications channel J and call the rescue vehicle he wished to communicate with -- but there was no guarantee that the specific rescue vehicle he was trying to reach would in fact be monitoring channel J (since the rescue vehicle driver would first have to change his channel selector to channel J as well). Central dispatchers often had the burden of manually directing the various different personnel to cross-group channels, and much time was wasted coordinating such efforts when emergency or disaster situations made time of the essence.
In contrast to the old crystal controlled fixed frequency systems, prior art trunked radio repeater systems rely upon preprogrammed group identifications rather than preset operating frequencies to provide the communications partitioning shown in FIG. 1. Trunked radio communications systems assign communications channels on an "as needed" basis for the exclusive use of calling mobile units requesting communications and to the group of mobile units being called. It is possible to provide much additional flexibility by pre-programming mobile units in advance with several different group identifications (thus making a given mobile unit a "member" of several different groups of transceivers). Since the number of groups the system can support is limited only by the RF signalling protocol providing identification of groups (and the programming capabilities of the mobile transceivers), it is possible to provide an almost arbitrarily large number of different logical groupings of transceivers -- for example, the assignee's signalling protocol disclosed in U.S. application Ser. No. 056,922 to Childress et al entitled "Trunked Radio Repeater System" filed Jun. 3, 1987 and U.S. application Ser. No. 181,441 to Childress entitled "Trunked Radio Repeater System" filed Oct. 7, 1987 provides for individual identification of each and every mobile transceiver in the field and supports over 4000 different groups.
This trunked arrangement provides for much additional flexibility. For example, referring again to FIG. 1, a first group might be formed by all members of police squad A; a second group might consists of all members of police squad A and B; a third group might consist of a subset of police squad A (e.g., certain detectives and a supervisor); a fourth group might consist of all police supervisors from squads A and B; and a fifth group might consist of all members of police squad A and all members of the rescue squad.
Even though all groups are in effect "reusing" the same communications channels in this trunked radio system, the trunking is mostly transparent to individual users. That is, when a police officer in police squad A switches his "channel" (actually group) selector switch to correspond to the first group and actuates his "push-to-talk" microphone switch to make a call, his transceiver and all other active transceivers of police squad A are automatically controlled to switch to a free "working" channel temporarily dedicated to their use -- and significantly, no other mobile transceivers are permitted to monitor or participate in the communications over this channel. This privacy feature afforded by trunked communications systems is important for providing each group of users with efficient, reliable communications, is critical for certain sensitive communications services (e.g., the police narcotics and detective squads) and is also critical for preventing interference from other users (e.g., the driver of a snow removal vehicle cannot interfere with communications between members of police squad A no matter what the snow truck driver does with his transceiver). Thus, in this respect the trunked system behaves from a user's view point like the prior systems in which each service had a channel dedicated to its exclusive use -- while providing the radio spectrum and cost economy derived from channel and repeater sharing.
In a trunked environment, compartmentalizing radio transceivers into groups is essential to effective, reliable, private communications. In the past, however, such compartmentalization resulted in serious inflexibility when special situations arose. In most prior systems, all groupings of radio transceivers had to be defined beforehand (e.g., by hardwiring or preprogramming at the time the transceivers were issued to users and placed in the field). For example, when a police officer in squad A was issued his radio transceiver, the transceiver would typically be preprogrammed to respond to calls for certain groups and to never respond calls for other groups. A disaster situation (plane crash, major fire, landslide, earthquake, etc.) or a special event (e.g., county fair, parade and the like) might require this police officer to communicate with other users he normally does not communicate with. For example, those assigned to crowd control at a special event such as a parade might include a squad A police officer, a rescue squad vehicle, several municipal vehicles, and an officer from police squad B. It would be highly desirable to permit these different users to communicate with one another over their own communications channel for the duration of the special event without disturbing or interfering with communications of the rest of the two police squads, the rescue squad and the municipal vehicles.
Prior trunked repeater systems sometimes provided the capability of combining several groups together into a large group via a multiple group call -- so that all members of, for example, police squad A, the rescue squad, all municipal vehicles and all members of police squad B could be collected onto a single communications channel in response to a single (typically dispatcher initiated) "multiple group call". The problem with this approach is that it involves too many radio users to be effective (i.e., many more than are needed for the necessary communications) -- and more seriously, may draw users not involved in the necessary communications away from other radio calls important to them. The only really effective way in the past to accomplish the desired result was extremely inconvenient and costly -- issuing each of the users a "floater" transceiver specially programmed for a spare group (and making sure they each returned their transceiver at the end of the special event).
The concept of "dynamic regrouping" in a trunked radio system is generally known. Dynamic regrouping allows a system operator to program customized group identifications into radio transceivers in the field from the central system facility at will -- and dynamically form special groups for special purposes. Disasters such as plane crashes, severe storms, major fires, landslides and earthquakes as well as special events are all examples where the ability to quickly reconfigure radios could be a valuable tool to the public safety officer. As an example, personnel involved in handling the crisis of a plane crash might include certain police officers, certain rescue vehicles, certain municipal vehicles and certain fire vehicles. It would be highly advantageous to provide some way to reconfigure the fixed, compartmentalized groups of transceivers normally provided by a trunked system to dynamically form special groups consisting only of these involved radio units -- while preserving the units' existing group classifications (and thus, in some cases, their capability to make routine calls) and also without disrupting any other communications taking place on the system.
The need for dynamic regrouping typically arises when dispatchers and field personnel are under tremendous pressure to perform under unpredictable conditions. The trunked communication system should help alleviate confusion rather than contribute to it -- so that if dynamic regrouping is to implemented at all, it must occur rapidly and predictably and in a fashion that can be monitored and controlled by any supervisor. It is especially important that activating a dynamically created group ("regroup") does not interfere with any ongoing radio communications in the field. Unfortunately, existing techniques for implementing dynamic regrouping have not met these demanding requirements and have therefore caused dynamic regrouping to remain in the realm of merely a great idea that cannot be practically implemented in the form of a usable tool.
Motorola, Inc. of Shaumburg, Ill., has developed a so-called "SMARTNET" trunked radio communications system which offers a limited dynamic regrouping capability. The optional dynamic regrouping capability provided in this 800 MHz trunked system allows the dispatcher to reassign radios into new talk groups without any mobile operator involvement to provide communications flexibility during emergency situations. Motorola's subscriber dynamic regrouping communications system is described in WO PCT Patent Publication No. 8701537 published Mar. 12, 1987 entitled "Method For Dynamically Regrouping Subscribers On A Communications System", and in press releases dated Aug. 6, 1987 and Jun. 27, 1986.
Briefly, the Motorola scheme provides for downloading a single dynamic reprogramming instruction to specified individual radio transceivers in the field via digital messages transmitted over the control channel to each of the transceivers individually. Upon receipt of the reprogramming message, the individual transceivers acknowledge the message, store the downloaded dynamic regroup identifier in an internal memory, and switch to a dynamic regroup mode in which they transmit and receive using the dynamic group instead of their old group(s). In another mode, a "group" dynamic regroup message is transmitted to an entire group of transceivers at a time in order to increase regrouping speed. The receiving transceivers begin using an alternate, fixed "dynamic code" previously programmed at time of manufacture and/or "personality PROM" programming. The units continue to use this "dynamic code" until dynamic regrouping messages cease being periodically transmitted over the control channel.
AmeriCom Corp. of Atlanta, Ga., has advertised an RF communications system featuring "over-the-air" reprogramming to add channels and reprogram mobiles without expensive ROM changes." This feature is described as providing more responsive service by dynamically reprogramming mobiles in order to lower service costs and permit real time "over-the-air" reprogramming of radio configurations and permissions.
The following issued U.S. Patents may also be generally relevant to the concept of dynamic regrouping:
Unfortunately, existing dynamic regrouping schemes (such as those described above) exhibit many practical problems when they are actually used in the real world. For example, existing techniques do not meet the demanding requirements of rapid and predictable regrouping which can be monitored and controlled by any supervisor -- and which does not interfere with ongoing radio communications in the field.
The user interface has been one of the more widely and strongly criticized elements in existing dynamic regrouping schemes. Some criticize the user interface itself and others criticize the entire regrouping process because it is too confusing to be of any value. Existing dynamic regrouping schemes require a supervisor to specify "regroups" (new, dynamically configured groups) from the "ground up" by keying in an identification for each and every individual radio transceiver to be placed in the regroup -- a difficult task to perform under time pressures of an emergency. Because dynamic regrouping changes the way the communications system operates on a very fundamental user level, for any practical and useful dynamic regrouping scheme the supervisor and the system dispatchers must be capable of: (a) accurately tracking -- on an interactive basis -- what radios are in what groups, (b) quickly assessing whether the regrouping process is proceeding in a suitable fashion or should instead be aborted or altered, and (c) easily altering regroup plans during activation or after they have been activated in response to changes in conditions and personnel. System supervisors and dispatchers must also be able to effectively handle and control communications during the regrouping process which, once initiated, causes entire groups to become fragmented and undefined until the process is complete. Existing dynamic regrouping systems simply do not meet these needs.
Additional complexity arises from the fact that most modern trunked communications systems serve a sufficiently large geographical service area to require multiple repeater sites -- and it is not possible to determine which users are being served by which sites at the time dynamic regrouping is activated. Existing dynamic regrouping systems provide no quick and efficient way to set up and execute dynamic regrouping plans having no conflicting regrouping requests relative to any of the mobile transceiver involved. Very serious problems could also arise in existing systems if a site controller fails either while radios are being dynamically regrouped or after they have been regrouped.
Another serious inadequacy of prior dynamic regrouping schemes is the lack of support offered to field personnel. For example, the capability of placing only one dynamically configured group assignment in a transceiver at any time is generally insufficient. In an emergency, key personnel must be able to switch between two or more of "regroups" -- but if their radio transceivers can accept only one regroup at a time, this switching is impossible. The police chief, the supervisors and other key personnel with the most knowledge, information and tactical experience become hamstrung because they are unable to participate in communications in more than one of the new dynamically configured groups.
Perhaps the most serious shortcoming of the existing dynamic regrouping schemes is that they often force users into "immature" groups for relatively long time periods. The dynamic regrouping process takes some time to complete in any system. An immature group is a group that is in the process of being formed by the regrouping process but because it is only partially formed, does not yet include enough transceivers to be an effective or usable group. The result is a temporary loss of communications effectiveness as transceivers are removed from existing groups and placed into a new group -- where they must wait for the regrouping process to reach some sufficient level of completion before effective communications can be established.
For example, assume an officer in the field is involved in a communique exchange and suddenly finds his transceiver automatically locked in a "regroup" with only one or two other transceivers. The system has not yet regrouped other radios into this new group, so he cannot yet communicate effectively in the new group -- and he also cannot communicate in the old group his transceiver was just removed from because the dynamic regrouping scheme has forced him into priority communications with the regroup. Meanwhile, the dispatcher has no idea at any given time who has or hasn't yet been regrouped, and therefore does not know what groups to talk to reach specific personnel. A solution to this problem offered by the prior art is to permit each transceiver to generate a "reprogram request" which the dispatcher must manually respond to. This is hardly an effective solution for the officer in the field during an emergency.
One way to lessen the bad "side effects" of the dynamic regrouping process is to make the occur as rapidly as possible. Unfortunately the task of reaching and remotely reprogramming, in a reliable manner, tens or hundreds of geographically scattered transceivers is a difficult task to accomplish at any speed, let alone as rapidly as possible. The flow of information from the regrouping terminal to the repeater site or sites, the rate at which transceivers can be regrouped, and the resulting loading of the digital control channel (which adds to existing control channel loading from other communications the system is supporting) are interrelated items that must work together effectively if the regrouping process is to proceed effectively. The regrouping process should occur as rapidly as possible to minimize the amount of confusion it creates. Unfortunately, existing dynamic regrouping schemes have not been designed with the real world in mind. Regrouping over the control channel limits the rate at which radios can be regrouped to only a few per second at best (due to the limited data transfer rate over the control channel and normal control channel loading). This limited regrouping rate is further aggravated by requiring the regrouping terminals to send initial requests via the control channel. Of course, multi-site configurations require regrouping terminals in the range of each individual site -- hardly an effective or efficient solution.
The present invention provides an improved dynamic regrouping scheme which includes an effective user interface, automatic support of multi-site systems, the capability to program individual radio transceivers with multiple new groups dynamically, a fast rate of reconfiguration, instantaneous switch over to prevent radios from residing in immature groups, and a satisfactory mode of operation should the site controller (or site controllers in non-fault tolerant systems) fail. Some of the features and performance specifications provided by the presently preferred exemplary embodiment of the present invention include: